Magnesium base alloys



United States Patent 0.

MAGNESIUM BASE ALLOYS Alfred Claude Jessup, Clifton Junction, near Manchester, England; Alma Jose Maria de Navarro, Henry James Huzzey Saunders, and Edward Frederick Emley, executors of said Alfred Claude Jessup, deceased, assignors to Magnesium Elektron Limited, Clifton Junction, near -Manchester, England, a British company No Drawing. 7 Application March 31, 1953, Serial No. 346,035

' Claims priority, application Great Britain May 9, 1951 Claims. (Cl. 75-168) This application is a continuation in part of my application Serial No. 227,542, filed May 21, 1951, now abandoned, for Improvements In or Relating to Magnesium Base Alloys.

This invention relates to magnesium base alloys of the kind containing small proportions of zirconium and zinc.

The development of such alloys in recent years has led to the production of alloys combining particularly high proof stress, ultimate tensile stress, and elongation in the cast state. Thus, for example, an alloy containing 0.5- 0.9% zirconium, 4-6% zinc, balance magnesium (known as Elektron Z5Z) has mechanical properties of the following order for test bars according to British Standard Specification L.101, Figure 1.

Ultimate 0.1% Proof Tensile Elongation Stress, t. s. 1. itresis, percent on 2" s.

test bars of this alloy.

0.1% Proof ,253,12 Elongation Stress, t. s. i. Stress, t. L percent on 2 No magnesium base alloys have hitherto been known which are capable of producing the combination of high mechanical properties of the magnesium-zirconium-zinc type of alloy quoted above with absence of microporosity and much reduced tendency to hot cracking. I have, however, now discovered a small range of alloys with which this highly desirable result is achieved.

According to the present invention the alloy has the following composition:

Magnesium At least 80 per cent Zinc 4-8 per cent Thorium At least 0.5 per cent Zirconium 0.5 to 0.9 per cent 2,750,288 Patented June '12, 1956 at least 0.5% zirconium beingin solution in thealloy and the ratio of thorium to zinc being not greater :than 3.5 :10 and not less than. 1:10 with or without any of the following:

Rare earth metals Up to 50% of the thorium content preferably not more than 25% of'the thorium content.

The alloys of the present invention have a maximum tensile stress higher than any magnesium-base alloys heretofore available commercially, for example, higher than those obtainable with Elektron Z5Z. The characteristic freedom from microporosity is particularly noticeable withthorium to zinc ratios between 0.15 and 0.35. With ratios below 0.15 this absence of microporosity is less marked and with ratios below 0.1 microporosity becomes difiicult to avoid in large castings having thick sections.

The alloys having thorium to zinc ratios between 0.25 and 0.35 are found to be readily weldable without cracking, and this characteristic is particularly marked in ratios from 0.3 to 0.35.

It is further found that the alloys with thorium to zinc ratios between 0.3 and 0.35 combine the advantages of weldability, high tensile stress and freedom from microporosity to a particularly remarkable extent which make them suitable for the production of large and complicated sand castings. These alloys having a zinc to thorium range of 0.3 to 0.35 also have, in the cast stage, a resistance to creep at elevated temperatures, e. g. up to 250 C., greater than any other known alloys of comparable tensile stress.

The alloys having a thorium to zinc ratio from 0.25 to 0.35 are particularly suitable for the production of large castings; thus finished machined castings having a weight of at least 50 lb. and with one or more sections having a thickness of at least half an inch can be produced in regular foundry practice with absence of microporosity, good weldability and average 0.1% proof stress of at least 8 tons per sq. inch and an average elongation of at least 8 per cent on 2 inches, these test figures being obtained by examination of sound testbars cut from the casting. A particularly important type of such casting consists of aircraft wheels in which these properties are especially desirable. Optimum properties have been obtained with alloys in the following range:

. 7 Percent Zinc 5.5-6.0 Thorium 1.6-1.9 Zirconium 1 0.6-0.9 Magnesium The remainder.

1 With at least 0.6 per cent dissolved in the alloy.

The following properties are quoted by way of example being taken from test bars in accordance with British Standard Specification 1 ..101, Figure 1, and heat treated 2 hours at 330 C., followed by 16 hours at 180 C.

Elongation 0.1 percent Elongation Composition i percent Treatment P. g percent on 2" t.s.1. on 2" 6% Zinc Longitudinal: 0.8% Th0r1um 10.7 19.1 12 11.6 18. 1 13. 5 ra 112 12-2 as C 1.27 Thorium. 10.8 19.0 14 5?; Zffggfi gattenmg 4 11.8 18.0 19.0 0.7% Zirconium 12. a 17. 9 19.0 6% Zine 11.8 17. 9 18.5 1.75% Thorium 10.8 18.2 10 10 12.0 18.3 18.5 0.7% Zirconium. Transverse:

14. 2 18.5 22.0 h 1 as After welg t attening or 4 13.8 In all three of these alloys microporosny was practically hrs. at 400 0 13.8 18.2 21.5 nil and the tendency to hot cracking very greatly reduced, F 3 i212 gig being much lower than in the Mg-Zn-Zr alloy previously referred to.

I have further found that the preferred proportion of zinc is from 5-6.5 per cent in which range quite outstanding properties are obtainable.

In addition to the adavntages above described the alloys of the present invention have a creep resistance at elevated temperatures better than that of the magnesium-zinczirconium alloys referred to.

The alloys of the present invention also have good fatigue properties, good corrosion resistance, and good castability.

The zirconium content, as already mentioned, should include at least 0.5 per cent dissolved in the alloy. The quantity of zirconium dissolved in the alloy is that quantity which is readily soluble together with the magnesium and Zinc in an aqueous solution of hydrochloric acid consisting of 10 ccs. HCl (specific gravity 1.16) and cos. of water per gram of the alloy.

The addition of rare earth metals to the alloys has the same tendency to embrittlement but a small proportion can be tolerated. As already mentioned, the proportion of rare earth metals should preferably not exceed onequarter of the thorium content and in any case should not exceed one-half of the thorium content.

The alloys preferably consist solely of magnesium-zincthorium and zirconium, and if desired, rare earth metals, although certain other additions can be tolerated as mentioned above.

The alloys may be subjected to solution heat treatment followed by precipitation heat treatment. For example a treatment at a temperature of 400-500 C. for 2-24 hours, followed by a treatment at 100-300 C. for 10-48 hours. It is, however, preferred to apply a treatment at a temperature of 300-350 C. for 1-5 hours followed by a treatment at 150250 C. for 10-24 hours. The alloys can, alternatively, be subjected to heat treatment at a single temperature, and in this case a temperature of 175 C.-32S C. over a period of 10-24 hours is suitable.

The alloys of the present invention not only give most satisfactory results in the cast state but also have excellent properties in the wrought condition. Thus, for example, extruded bars of 4" diameter in an alloy containing 5.7 per cent zinc, 1.8 per cent thorium, 0.7 per cent zirconium have given the following mechanical properties:

Again, rolled sheet of the thickness of 0.048" in-an alloy containing 5.7 per cent zinc, 1.6 per cent thorium and 0.7 per cent zirconium has given the following values:

All the above mentioned alloys possess a resistance to creep at elevated temperatures superior to that shown by any known magnesium base alloy with equivalent room temperature mechanical properties or even with room temperature mechanical properties approaching the very high values of proof stress ultimate stress and elongation shown by cast and wrought alloys according to the present invention.

We claim:

1. An alloy consisting apart from impurities of the followmg: Per cent by weight Zinc 5 to 6.5 Thorium at least 0.5 Zirconium 0.5 to 0.9 Magnesium Remainder.

at least 0.5 per cent zirconium being in solution in the alloy and the ratio of thorium to zinc being not greater than 3.5: 10 and not less than 1:10.

2. An alloy as claimed in claim 1 wherein the ratio of thorium to zinc is less than 3.0 to 10.

3. An alloy as claimed in claim 1 wherein the ratio of thorium to zinc is less than 2.5 to 10.

4. A11 alloy as claimed in claim 1 containing also one or more of the following: Rare earth metals Up to 50 per cent of the thorium content Beryllium Up to 0.01 per cent Calcium Up to 0.2 per cent Silver Up to 1 per cent Copper Up to 1 per cent Mercury Up to 1 per cent Lead Up to 1 per cent Thallium Up to 1 per cent Lithium Up to 1 per cent 5. A magnesium-base alloy, consisting, apart from impurities, of the following: Per cent by weight Zinc 5.5-6.0 Thorium 1.6-1.9 Zirconium 1 0.6-0.9 Magnesium The remainder.

At least 0.6 per cent being dissolved in thealloy.

References Cited in the file of this patent Serial No. 369,824, Sauerwald et al. (A. P. C.), published June 15, 1943, abandoned.

Leontis: Effect of Zirconium on Magnesium-Thorium and Magnesium-Thorium-Cerium Alloys, published in Journal of Metals, June 1952, pages 633-642. 

1. AN ALLOY CONSISTING APART FROM IMPURITIES OF THE FOLLOWING: 